Thrust magnitude of a lunar lander is discussed in this paper. Most fuel of a lunar lander is consumed in a powered descending phase from a lunar parking orbit to a landing point on the moon surface. Therefore, it is important to reduce the fuel consumption in this phase. The trajectories in the phase are designed using optimal control theory as solutions of minimum fuel consumption problem in this paper. The results of numerical calculations show that the optimum thrust exists. Moreover, the optimum non-dimensional thrust, the ratio of maximum thrust and hovering thrust, is almost same against the different parameters in equations of motion and initial conditions.
For future space transportation missions beyond earth orbit, propulsion systems applying cryogenic propellants can achieve efficient and rapid in-space mass transfer with high specific impulse. Refilling of cryogenic propellant generated on Moon surface also enhances the advantage. In this study, we propose a new cryogenic liquid rocket engine system for efficient multiple ignitions for such missions. Two engine operation modes, high-specific-impulse idle mode and low-pump-rotation throttling mode, are discussed using newly developed cycle analysis tool. State-of-the-art electric motor driven valves which continuously control the flow rates can realize these operation modes. The cycle analysis was conducted based on the expander bleed cycle considering combustion and turbopump instabilities and chamber wall temperature limit. The analytical results show the high-specific-impulse idle mode can offer higher specific impulse comparing to the conventional operation. During the low-pump-rotation throttling mode, the discharged propellant is used for tank pre-pressurization; therefore, helium consumption for tank pre-pressurization can be drastically reduced. Possible operational points with high specific impulse were found in the low-pump-rotation throttling mode with additional valve and piping to maintain the pump flow coefficient. These new engine operation modes offer less chill-down and helium consumption before ignitions and result in efficient in-space orbital transportation.
Hovering performance of a winged helicopter with side propellers is investigated experimentally. It is found that the wing download, which is one of the most critical factors for the hovering performance, is increased with the use of side propellers and that the increment of the wing download changes depending on the experimental parameters, which are wing incidence angle, wing flap angle, side propellers arrangement, and side propellers rotation direction. Although it is limited to the particular operational condition (hovering) and to the experimental parameters changed here, we propose an advantageous configuration of the winged helicopter with side propellers. How the side propellers influence the wing download and why the impact of the side propellers depends on settings of experimental parameters is discussed with reference to the results of CFD analysis.
Morphing wings have various possibilities to realize drag and noise reduction and to extend flight envelope by smoothly changing wing shape during flight. This study focuses on the application of Shape Memory Alloy (SMA) wires as a lightweight actuation mechanism for morphing wings because SMA has a large recovery stress per unit mass. To achieve the required actuation stroke for the SMA wires, it was considered to design the spiral configuration of the SMA wires. This research experimentally observes the relationship between the recovery strain as the actuation performance of tube-guided wires and its geometric parameters such as spiral angle. It was found that the friction force between the SMA wire and its spirally guiding tube plays an important role on the actuator performance, and the performance gradually decreased as the length of the wires and the number of spirals increased. Furthermore, the application of the spiral configuration of SMA wire for a small aircraft was investigated. As a result, the effectiveness depends on the coefficient of the friction between the SMA wire and the spiral tube. Thus, the results obtained in this study could be used to properly design the tube-guided SMA coil-type actuators for morphing wings considering the effectiveness and challenges in its implementation.